I personally unbind all the ctrl-# and alt-# keys on my alts.

This allows me to use a # on all clients and allow some to ignore the command at the macro level, saves slot assignments on your UI(s).

I.e. fireball is the primary command here (2)

/cast [modifier:alt,exists,harm,nodead] Scorch // I typically don't use Scorch on trash and if i'm about to fight a boss he's always pretargeted anyway.
/stopmacro [modifier:alt]
/cast [exists,harm,nodead] Fireball
/stopmacro [exists,harm,nodead]
/assist whoever (Focus, party1, etc.)
/cast [exists,harm,nodead] Fireball

I do the same for some of my CC commands

/stopcasting [modifier:alt]
/cast Counterspell [modifier:alt] // I pretty much only use this when my mages have an active caster target
/stopmacro [modifier:alt]
/stopcasting [modifier:ctrl, target=focus, exists, harm, nodead]
/cast Counterspell [modifier:ctrl, target=focus, exists, harm, nodead]

Second macro is useful for fights like R&J in Opera where you can't CC a caster but need to be able to interrupt it's spells